Piston Pump With Improved Efficiency

ABSTRACT

The present invention relates to a piston pump for delivering hydraulic fluid, including a reciprocating piston for building up pressure in a pressure chamber; a sealing element is situated on the piston; during a compression phase, this sealing element produces a seal between the pressure chamber and a low-pressure region of the piston pump and during an intake phase, it opens a connection between the pressure chamber and the low-pressure region in order to draw hydraulic fluid into the pressure chamber.

PRIOR ART

The present invention relates to a piston pump for delivering hydraulic fluid with improved efficiency in which the piston pump is particularly inexpensive to manufacture.

A wide variety of piston pump designs are known from the prior art. Piston pumps for vehicle brake systems are frequently embodied in the form of radial piston pumps, in which at least one piston can be set into a reciprocating motion by means of a cam. Piston pumps of this kind are frequently used in connection with electronic stability systems (ESP) or electrohydraulic brake systems (EHB). Since the use of such systems is on the rise, even in smaller vehicles, it is necessary for the piston pumps to be very inexpensive to manufacture. Another requirement for such piston pumps is that they be as small and lightweight as possible. Since future brake systems will operate with higher pressures, the piston pump must also be able to generate these desired pressure levels.

The known piston pumps are usually equipped with a pressure chamber situated between an inlet valve and an outlet valve; the movement of the piston builds up an operating pressure in this pressure chamber. At its end oriented toward the piston, this pressure chamber must be sealed in relation to a low-pressure region of the piston pump. This is frequently accomplished by means of piston rings or sealing elements situated inside the cylinder. The inlet valve is situated in the pressure chamber and a supply line of hydraulic fluid can be provided by means of conduits integrated into the piston. The pressure chamber also contains a spring for returning the piston to its initial position; this placement of the spring can result in unfavorable flow conditions in the pressure chamber and in particular, can lead to problems due to gas evolution from the gases combined in the hydraulic fluid, and can also lead to noise problems.

ADVANTAGES OF THE INVENTION

The piston pump for delivering hydraulic fluid according to the present invention, with the defining characteristics of claim 1, has the advantage over the prior art that it is particularly compact and requires fewer parts. This enables a particularly inexpensive production of the piston pump according to the invention. According to the invention, this is achieved by the fact that a sealing element situated on the piston simultaneously also performs the function of the inlet valve. This makes it possible to reduce the number of parts and to achieve a particularly compact design of the piston pump. The sealing element is embodied in such a way that during a compression phase, its seals the pressure chamber in relation to a low-pressure region of the piston pump and during an intake phase, it produces a connection to the low-pressure region in order to draw hydraulic fluid into the pressure chamber.

Preferred modifications of the invention are disclosed in the dependent claims.

Preferably, the sealing element is situated on the piston so that it has an axial play. In other words, the position of the sealing element in relation to the piston can be changed in the axial direction of the piston by the amount of the axial play. This makes it possible to achieve a particularly simple embodiment for the combined inlet valve/sealing element. The sealing element can consequently assume two positions in relation to the piston, namely a first position for the intake phase and a second position for the compression phase.

In a particularly preferable embodiment, the sealing element on the piston is situated in a stepped region provided at the pressure chamber end region of the piston.

According to a preferred embodiment of the invention, the sealing element is embodied in such a way that its inner circumference has at least one raised region and one recessed region. During the intake phase, this permits an overflow of the sealing element along the recessed region between the sealing element and the piston. In a particularly preferred embodiment, the inner circumference of the sealing element is provided with a number of plane-like raised regions and a number of plane-like recessed regions situated between the raised regions. It is particularly preferable in this case for the arrangement of the raised and recessed regions to be symmetrical. This makes it possible to assure symmetrical pressure conditions against the sealing element. The size and depth of the recessed regions depends on the one hand on the inner diameter of the sealing element and on the other hand, also depends on the desired intake volume and stroke length of the piston.

In order to be able to achieve an intake of the piston pump as quickly as possible after the direction reversal of the piston once the top dead center has been reached, the inner circumference of the sealing element has a bevel on the edge oriented toward the low-pressure region of the piston pump. This bevel facilitates the opening of the sealing element for the intake phase, thus permitting a very short reaction time for the inlet function of the sealing element. It should be noted that it is also possible to provide a bevel on the inner circumference of the sealing element, at the edge oriented toward the pressure chamber. This makes it possible to improve guidance of the sealing element on the piston.

It is also preferable to provide a spring element in order to exert a spring force on the sealing element in the axial direction. In particular, this makes it possible to achieve an improved sealing by means of the sealing element during the compression phase of the piston pump. The spring element is preferably embodied in the form of a leaf spring with one or more spring tabs. Affixing the spring element to the piston in a preferable fashion achieves a particularly compact design. The spring element can, for example, be affixed to the piston by means of a plate-shaped retaining element; the retaining element is affixed to the pressure chamber end of the piston and protrudes beyond the stepped region of the piston in order to support the spring element.

Preferably, the piston has at least one flattened region on the circumference in order to supply hydraulic fluid from the low-pressure region to the sealing element. Preferably, three flattened regions are provided on the piston, each spaced equidistantly apart from adjacent flattened regions along the circumference of the piston.

In order to further improve efficiency, preferably a return spring for returning the piston to its initial position is situated outside the pressure chamber. Since the sealing element that performs the function of the inlet valve is also not situated in the pressure chamber, it is thus possible to obtain a clearance-optimized pressure chamber. Consequently, the pressure chamber can be easily designed for the desired pressure conditions and can have a simple geometry. According to the invention, a cylinder element is preferably provided for this, against the inside of which the sealing element is guided and against the outside of which the return spring for the piston is guided. The return spring in this case can be supported on the piston against an additional stepped region or against protruding projections. According to another preferred embodiment of the invention, the return spring is embodied in the form of a tapering, in particular conical spiral spring, which rests against a circumferential groove provided on the piston.

According to another preferred embodiment of the invention, the return spring for the piston is situated in a cam chamber of the piston pump. This, too, makes it possible to situate the return spring outside the pressure chamber of the piston pump. The return spring in the cam chamber is preferably fastened to the piston and particularly preferably, is embodied in the form of a leaf spring, which is supported against the walls of the cam chamber.

It is particularly preferable to use the piston pump according to the present invention in brake systems of motor vehicles, for example to control and regulate a pressure in a wheel brake cylinder. It is particularly preferable for the piston pump according to the present invention to be used in connection with electronic control and regulating systems of the brake system, e.g. ESB, EHB, TCS, etc. Since the piston pump according to the present invention is particularly inexpensive to produce, it is possible to significantly reduce the costs for equipping even small vehicles with such brake systems.

DRAWINGS

Preferred exemplary embodiments of the invention will be described below in conjunction with the accompanying drawings.

FIG. 1 is a schematic sectional view of a piston pump according to a first exemplary embodiment of the present invention,

FIG. 2 is a perspective view of several individual parts of the piston pump shown in FIG. 1,

FIGS. 3 a to 3 c show various views of a sealing ring according to the first exemplary embodiment of the present invention,

FIGS. 4 a and 4 b show schematic views of a spring element for exerting a spring force on the sealing element,

FIG. 5 shows an enlarged partial cross section through the piston pump of the first exemplary embodiment during the intake phase,

FIG. 6 is an enlarged, partial cross-sectional view of the piston pump of the first exemplary embodiment during the compression phase,

FIG. 7 is a schematic sectional view of a piston pump according to a second exemplary embodiment of the present invention, and

FIG. 8 is a schematic sectional view of a piston pump according to a third exemplary embodiment of the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

A piston pump 1 according to a first exemplary embodiment of the present invention will be described below in conjunction with FIGS. 1 through 6.

As shown in FIG. 1, the piston pump 1 has a piston 3 contained in a housing 2. The housing 2 has a stepped bore 2 a to accommodate the piston 3. The piston 3 is driven by means of a cam 22 that is situated in the cam chamber 21 and whose rotation direction is indicated by the arrow D.

The piston 3 is depicted in detail in the perspective view in FIG. 2. As is clear from the drawing, the end of the piston 3 oriented toward the pressure chamber has a stepped region 3 a and three flattened regions 3 b situated along the circumference of the piston. As is particularly clear from FIGS. 1, 5, and 6, a sealing element 4 is situated on the stepped region 3 a. The sealing element 4 is affixed to the stepped region 3 a of the piston 3 by means of a spring element 7 and a plate-shaped retaining element 8. The plate-shaped retaining element 8 is fastened by being press-fit in a recess 3 d of the piston by means of an annular fastening region.

The piston pump 1 also includes a pressure chamber 9, which is situated between the sealing element 4 and an outlet valve 11. According to the invention, the sealing element 4 is provided as an inlet valve element for supplying hydraulic fluid, as will be described later. The outlet valve 11 has ball 12 and a return spring 13. The return spring 13 is supported in a stopper element 14; the stopper element 14 seals the stepped bore 2 a of the housing 2 in a fluid-tight fashion. Downstream of the outlet valve 11, there are two pressure lines 15 to which the pressurized fluid from the pressure chamber 9 is supplied.

As is particularly clear from FIG. 1, a cylinder element 10 is situated between the outlet valve 11 and the pressure chamber 9. The cylinder element 10 includes a plate-shaped base region 10 a with a flange-like cylinder ring 10 b integrally joined to it. The cylinder ring 10 b has an inner circumference surface 10 c and an outer circumference surface 10 d. The cylinder element 10 also has a central through opening 10 e that is opened and closed by means of the outlet valve 11.

In order to return the piston 3 to its initial position, a return spring 16 is provided, which is supported against the cylinder element 10 at one end and is supported against a raised region 3 c on the piston 3 at the other (see FIG. 1).

The housing 2 also contains supply lines 17, which supply hydraulic fluid to a low-pressure region 18. As it is clear from FIG. 1, the return spring 16 for the piston 3 is likewise situated in the low-pressure region 18 of the piston pump. In order to provide a seal in relation to the cam chamber 21, the piston 3 is also provided with a sealing ring 19 and a guide ring 20, which are situated in a groove-shaped recess in the piston.

The sealing ring according to the invention will be described below in conjunction with FIGS. 3 a, 3 b, and 3 c. FIG. 3 a is a top view of the sealing ring 4. As is clear from FIG. 3 a, the sealing ring 4 is embodied in the form of a closed ring and on its inner circumference, has four raised regions 5 and four recessed regions 6. The raised regions 5 and recessed regions 6 are each embodied as plane-like. FIG. 3 b is a sectional view of the sealing element 4, cut along the line IV-IV. As is clear from FIG. 3 b, relatively wide bevels 5 a are provided in the region of the sealing element 4 oriented toward the low-pressure side and relatively wide bevels 5 b are provided in the region of the sealing element 4 oriented toward the pressure chamber. In particular, the bevels 5 a on the low-pressure side permit the sealing element 4 to rapidly react when it is to perform the function of an inlet valve.

As is clear from FIGS. 5 and 6, the sealing element 4 is situated on the stepped region 3 a of the piston 3 in such a way that it is able to move in the axial direction X-X of the piston with a predetermined amount of play S. The movement of the sealing element 4 is limited on the one hand by the stepped region 3 a and on the other hand by the retaining element 8, which is affixed to the piston 3 and has a larger diameter than the stepped end of the piston 3 oriented toward the pressure chamber. As is clear from FIGS. 5 and 6, the spring element 7 is also situated between the retaining element 8 and the sealing element 4. The spring element 7 is shown in the detailed views in FIGS. 4 a and 4 b and is a leaf spring-like spring element with an annular base region 7 a and a number of spring tabs 7 b. In this exemplary embodiment, there are six spring tabs 7 b. The spring element 7 exerts a spring force on the sealing element 4 in the axial direction X-X.

The sealing element 4 is preferably manufactured of a plastic material, in particular PA66 or PEEK, or of a ceramic material.

The operation of the piston pump 1 according to the present invention will be described below in accordance with the first exemplary embodiment. The operation of the piston pump 1 will be described in particular with reference to FIGS. 5 and 6. FIG. 5 shows the beginning of the intake phase of the piston pump, in which the piston 3 moves in the direction of the arrow A. During the intake phase, the sealing element 4 is situated in the first position shown in FIG. 5 so that hydraulic fluid in the low-pressure region 18 can overflow the sealing element 4. This is indicated by the arrows in FIG. 5. The outlet valve 11 is in its closed position. The hydraulic fluid from the low-pressure region 18 overflows the sealing element 4 along the recessed regions 6 on the inner circumference of the sealing element 4 and then travels through the interstices between the spring tabs 7 b of the spring element 7 and into the pressure chamber 9. The spring tabs 7 b thus serve as a stop for the sealing element 4 so that between the plate-shaped retaining element 8 and the sealing element 4, an intermediate space remains open, through which the hydraulic fluid can flow into the pressure chamber 9. The spring element 7 does in fact exert a spring force F_(F) on the sealing element in the movement direction A of the piston, but this spring force is less than the friction force F_(K) between the sealing element 4 and the inner circumference 10 c of the cylinder element 10, which acts in opposition to the spring force. Consequently, the sealing element 4 is situated in the position shown in FIG. 5 during the intake phase of the piston pump in order to draw in hydraulic fluid.

After the piston 3 reaches its bottom dead center, the movement direction of the piston reverses and it moves in the direction of the arrow B (see FIGS. 1 and 6). The movement reversal of the piston in the direction of the arrow B also changes the direction of the friction force F_(K) between the sealing element 4 and the inner circumference 10 c of the cylinder element 4 so that the sealing element 4 rests against the stepped region 3 a of the piston. FIG. 6 shows this state. Consequently, the sealing element 4 according to the present invention makes it possible that, after the piston 3 reverses direction once it reaches its bottom dead center, the connection between the pressure chamber 9 and the low-pressure region 18 is closed since the sealing element 4 produces a seal against both the inner circumference 10 c of the cylinder element 10 and the stepped region 3 a of the piston 3. When the piston 3 moves farther in the direction of the arrow B, then a continuously increasing pressure builds up in the pressure chamber 9. As a result, the outlet valve 11 remains closed until the pressure in the pressure chamber 9 is greater than the pressure in the pressure lines 15. As soon as the pressure in the pressure chamber 9 exceeds the pressure in the pressure lines 15, then the outlet valve 11 opens so that the connection between the pressure chamber 9 and the pressure lines 15 via the through opening 10 e is opened. FIG. 6 shows this open state. During the compression phase of the piston pump, the spring force F_(F) of the spring element 7 in the axial direction X-X of the piston 3 consequently acts on the sealing element 4 in addition to an axial force F_(A) exerted by the pressurized hydraulic fluid in the pressure chamber 9. Moreover, the hydraulic fluid in the pressure chamber 9 also acts against the recessed regions 6 on the inner circumference of the sealing element 4, thus also exerting a radial force FR on the sealing element 4 during the compression phase. It is consequently possible to achieve an improved sealing by making use of the compression forces of the hydraulic fluid present in the pressure chamber 9.

Consequently, providing the axial play S of the sealing element 4 in relation to the piston 3 makes it possible for the sealing element 4 to perform both the sealing function between the pressure chamber 9 and the downstream pressure region 18 during the compression phase of the piston pump and the inlet valve function during the intake phase. As a result, it is no longer necessary to provide a separate inlet valve for the pressure chamber 9; instead, a single component performs both functions. The overflow of the sealing element 4 during the intake phase occurs along the inner circumference. It should be noted that for a uniform pressure distribution on the sealing element 4, the raised regions 5 and the recessed regions 6 are preferably situated symmetrically in relation to the central axis of the sealing element.

Providing wide bevels 5 a at the edges of the raised regions 5 oriented toward the low-pressure side and bevels 5 b at the edges of the raised regions 5 oriented toward the pressure side improves the reaction behavior of the sealing element 4 during the transition from the intake phase to the compression phase and from the compression phase to the intake phase. This makes it possible to reduce the losses in the piston pump 1 and improve efficiency. In addition, the invention's placement of the return spring 16 of the piston 3 outside the pressure chamber 9 makes it possible to optimize the geometry of the pressure chamber 9 since it is not necessary for a piston return element to be situated in the pressure chamber. In particular, this makes it possible to achieve improved flow conditions in the pressure chamber 9.

Since the return spring 16 for the piston 3 is situated outside the pressure chamber 9, it is also possible to achieve a noise reduction since there is a reduction in the risk of gas evolution from the gases contained in the hydraulic fluid in the region of the pressure chamber 9. This also reduces the risk of a delivery stoppage of the pump due to larger quantities of gas in the pressure chamber 9.

It should also be noted that the piston pump according to the invention is very easy to assemble since on the one hand, the number of parts can be reduced and on the other hand, for example, the sealing element 4 can be premounted onto the piston 3 along with the spring element 7 and the retaining element 8. In this case, the retaining element 8 can be fastened into the recess 3 d of the piston 3 by means of a press fit or by means of caulking.

A piston pump 1 according to a second exemplary embodiment of the invention will be described below in conjunction with FIG. 7. Parts that are the same or are functionally equivalent have been provided with the same reference numerals as in the first exemplary embodiment.

The piston pump 1 of the second exemplary embodiment corresponds essentially to that of the first exemplary embodiment; instead of a cylindrical return spring 16, in the second exemplary embodiment, a tapering return spring 16 is used. The end of the reliably tapering return spring 16 oriented toward the pressure chamber once again rests against the cylinder element 10 while the end of the tapering return spring 16 oriented toward the cam rests against a circumferential groove 23 provided in the piston 3. This simplifies the manufacture of the piston 3 since it is no longer necessary, as in the first exemplary embodiment, to provide three raised regions 3 c to support the cylindrical return spring. It is particularly preferable for the tapering return spring 16 of the second exemplary embodiment to be wound directly onto the piston 3 so that the installation of the return spring 16 onto the piston 3 can be automated. The piston pump 1 from FIG. 7 is depicted in the compression phase; the outlet valve 11 is still closed and the pressure in the pressure chamber 9 continuously increases as the movement of the piston 3 continues toward its top dead center.

After the return spring 16 is wound on, the sealing element 4, together with the spring element 7, is fastened to the piston 3 during attachment of the retaining element 8 and then this assembly is installed in the housing 2 together with the cylinder element 10. Otherwise, this exemplary embodiment corresponds to the first exemplary embodiment so that reference can be made to the description given in conjunction therewith.

FIG. 8 shows a piston pump 1 according to third exemplary embodiment of the present invention. Parts that are the same or are functionally equivalent have once again been provided with the same reference numerals as in the first exemplary embodiment.

As in the preceding exemplary embodiments, in the third exemplary embodiment, the sealing element 4 is likewise embodied in the form of an inlet valve. FIG. 8 shows the piston pump 1 during its intake phase. But in the third exemplary embodiment, the return spring for the piston 3 is embodied in the form of a leaf spring, which is situated in the cam chamber 21 of the piston pump 1. The leaf spring 24 is fastened in a groove 26 in the piston 3 situated at the cam end of the piston 3 and is supported against the wall of the cam chamber 21.

Situating the return element in the cam chamber 21 also makes it possible to eliminate the cylinder element 10 of the preceding exemplary embodiments. As is clear from FIG. 8, the sealing element 4 seals directly against a part of the stepped bore 2 a in the housing 2. In lieu of the cylinder element 10 in the preceding exemplary embodiments, therefore, it is only necessary to provide a plate 25 to delimit the pressure chamber 9, which plate has a through opening 25 a in the middle that is opened and closed by the outlet valve 11. It is thus possible to further reduce the number of parts in the piston pump 1 according to the third exemplary embodiment, in particular permitting a further reduction in the manufacturing and assembly costs. Otherwise, the third exemplary embodiment corresponds to the preceding exemplary embodiments so that reference can be made to the description given in conjunction therewith. 

1-18. (canceled)
 19. A piston pump for delivering hydraulic fluid, the pump comprising a reciprocating piston for building up pressure in a pressure chamber; a sealing element on the piston this sealing element producing a seal between the pressure chamber and a low-pressure region of the piston pump during a compression cycle and opening a connection between the pressure chamber and the low-pressure region in order to draw hydraulic fluid into the pressure chamber during an intake phase.
 20. The piston pump according to claim 19, wherein the sealing element has an axial play on the piston.
 21. The piston pump according to claim 19, wherein the sealing element on the piston is situated in a stepped region of the piston.
 22. The piston pump according to claim 19, further comprising at least one raised region and at least one recessed region on an inner circumference of the sealing element in order to permit an overflow of the sealing element along the recessed region during the intake phase of the piston pump.
 23. The piston pump according to claim 22, wherein said at least one raised region and at least one recessed region comprise a plurality of plane-like raised regions that are separated from one another by means of an equal number of interposed plane-like recessed regions.
 24. The piston pump according to claim 19, further comprising a bevel on the inner circumference of the sealing element, at the edge oriented toward the low-pressure region.
 25. The piston pump according to claim 22, further comprising a bevel on the inner circumference of the sealing element, at the edge oriented toward the pressure chamber.
 26. The piston pump according to claim 19, further comprising a spring element exerting a spring force on the sealing element in the axial direction of the piston.
 27. The piston pump according to claim 26, wherein the spring element is a leaf spring with a number of protruding spring tabs.
 28. The piston pump according to claim 26, wherein the spring element is affixed to the piston.
 29. The piston pump according to claim 27, wherein the spring element is affixed to the piston.
 30. The piston pump according to claim 26, further comprising a plate-shaped retaining element fastened to the piston and supporting the spring element.
 31. The piston pump according to claim 27, further comprising a plate-shaped retaining element fastened to the piston and supporting the spring element.
 32. The piston pump according to claim 19, further comprising at least one flattened region on the circumference of the piston providing a flow path for hydraulic fluid from the low-pressure region to the sealing element.
 33. The piston pump according to claim 19, further comprising a cylinder element having a cylindrical region, the sealing element resting against the inside of the cylindrical region.
 34. The piston pump according to claim 19, further comprising at least one integrally embodied region on the piston, and a return spring for the piston engaging the at least one integrally embodied region.
 35. The piston pump according to claim 34, wherein the at least one integrally embodied region for supporting the return spring for the piston comprises a circumferential groove, and wherein the return spring is embodied in the form of a tapering spiral spring.
 36. The piston pump according to claim 19, further comprising a return spring for returning the piston to its initial position, the return spring being located in a cam chamber.
 37. The piston pump according to claim 36, wherein the return spring is a leaf spring, which is affixed in a groove in the piston.
 38. A brake system or stability system for a vehicle, including a piston pump according to claim
 19. 